U.S. patent number 5,804,087 [Application Number 08/646,817] was granted by the patent office on 1998-09-08 for method of adjusting natural frequency of dual-axis vibratory structure.
This patent grant is currently assigned to Korea Advanced Institute of Science and Technology, Samsung Electronics Co., Ltd.. Invention is credited to Young-ho Cho, Ki-bang Lee, Ci-moo Song.
United States Patent |
5,804,087 |
Lee , et al. |
September 8, 1998 |
Method of adjusting natural frequency of dual-axis vibratory
structure
Abstract
There is provided a method of adjusting the natural frequency of
a dual-axis vibratory structure having: a first spring member
having a lengthwise direction coinciding to a first axis direction
receiving an electrostatic force; a second spring member having a
lengthwise direction coinciding to a second direction perpendicular
to the first axis direction and having a width narrower than that
of the first spring member; and a mass portion, the method
comprising the steps of: measuring the natural frequencies relative
to the first axis direction of the vibratory structure and a third
axis direction perpendicular to a plane formed by the first and
second axes; varying the thickness of the first spring member so as
to adjust the natural frequency of the third axis direction while
fixing the natural frequency of the first axis direction; and
repeating the measuring step and the thickness varying step until
the natural frequency of the first and third axes directions are
within the scope of a permissible error. The method can be adjusted
to coincide the natural frequency of the vibratory structure with a
design value, so that linearity and the sensitivity of a sensor are
improved and operation bandwidth increases.
Inventors: |
Lee; Ki-bang (Seoul,
KR), Cho; Young-ho (Daejeon, KR), Song;
Ci-moo (Sungnam, KR) |
Assignee: |
Samsung Electronics Co., Ltd.
(Kyungki-do, KR)
Korea Advanced Institute of Science and Technology (Taejon,
KR)
|
Family
ID: |
19415388 |
Appl.
No.: |
08/646,817 |
Filed: |
May 21, 1996 |
Foreign Application Priority Data
|
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|
|
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May 25, 1995 [KR] |
|
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1995-13256 |
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Current U.S.
Class: |
216/41;
438/52 |
Current CPC
Class: |
G01C
19/5769 (20130101) |
Current International
Class: |
G01C
19/56 (20060101); H01L 022/027 () |
Field of
Search: |
;216/2,41 ;437/228 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Breneman; R. Bruce
Assistant Examiner: Adjodha; Michael
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
L.L.P.
Claims
What is claimed is:
1. A method of adjusting the natural frequency of a dual-axis
vibratory structure having: a first spring member having a
lengthwise direction coinciding to a first axis direction receiving
an electrostatic force; a second spring member having a lengthwise
direction coinciding to a second direction perpendicular to the
first axis direction and having a width narrower than that of the
first spring member; and a mass portion, said method comprising the
steps of:
measuring the natural frequencies relative to the first axis
direction of the vibratory structure and a third axis direction
perpendicular to a plane formed by the first and second axes;
varying the thickness of the first spring member so as to adjust
the natural frequency of the third axis direction while fixing the
natural frequency of the first axis direction; and
repeating said measuring step and said thickness varying step until
the natural frequencies of the first and third axes directions are
within the scope of a permissible error.
2. A method of adjusting the natural frequency of a dual-axis
vibratory structure according to claim 1, wherein said
thickness-varying step includes the step of decreasing the
thickness of the first spring member, when the natural frequency of
the third axis direction of the structure is higher than that of
the first axis direction.
3. A method of adjusting the natural frequency of a dual-axis
vibratory structure according to claim 1, wherein said
thickness-varying step includes the step of increasing the
thickness of the first spring member, when the natural frequency of
the third axis direction of the structure is lower than that of the
first axis direction.
4. A method of adjusting the natural frequency of a dual-axis
vibratory structure according to claim 2, wherein said
thickness-decreasing step is executed by one of reactive ion
etching, plasma etching and sputtering.
5. A method of adjusting the natural frequency of a dual-axis
vibratory structure according to claim 3, wherein said
thickness-increasing step is executed by one of sputtering
deposition, ion beam sputtering deposition,
electron-cyclotron-resonance sputtering deposition, ion-plating,
molecular beam epitaxy, chemical vapor deposition, and metal
organic chemical vapor deposition.
6. A method of adjusting the natural frequency of a dual-axis
vibratory structure according to claim 1, wherein said
thickness-varying step is executed by using a mask formed with an
aperture corresponding to a region for realizing a thickness
variation in the first spring member and by varying the thickness
of the first spring member under the aperture.
7. A method of adjusting the natural frequency of a dual-axis
vibratory structure, for use in a gyroscope, having: a first spring
member of a first axis direction coinciding with the direction
receiving an electrostatic force; a second spring member of a
second axis direction perpendicular to the first direction having a
width narrower than that of the first spring member; and a mass
portion, said method comprising the steps of:
measuring the natural frequency relative to the first axis
direction and the third axis direction perpendicular to a plane
formed by the first and second axes of the vibratory structure;
varying the thickness of the first spring member of the first axis
direction so as to adjust the natural frequency of the third axis
direction, while fixing the natural frequency of the first axis
direction; and
repeating said measuring step and said thickness varying step until
the natural frequency of the first axis direction and the third
axis direction is within the scope of a permissible error.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of adjusting the natural
frequency of a dual-axis vibratory structure, and more
particularly, to a method of adjusting the natural frequency of a
dual-axis vibratory structure by increasing or decreasing the
thickness of part of the vibratory structure through deposition or
etching process.
It is a very important technology to correct the natural frequency
of a dual-axis vibratory structure so that it can vibrate with a
specific natural frequency, and the technology is applied to a
surface acoustics wave (SAW) filter and a crystal oscillator used
in a humidifier, for example. Since common crystal oscillators or
SAW filters vibrate with a single vibrating mode, the natural
frequency thereof can be comparatively easily adjusted by using a
method of adjusting a frequency according to conventional
technology. However, since a dual-axis vibratory structure
oscillating with two oscillating modes is not easily adjusted with
the conventional frequency adjusting method, a new method of
adjusting the frequency is needed.
The uses of dual-axis vibratory structures have expanded recently.
A representative one among various articles using a dual-axis
vibratory structure is a gyroscope. The gyroscope can play the role
of an angular velocity sensor for detecting an angular velocity or
an acceleration of an inertial body and has been used as a kernel
parts of a navigation device of a missile, a ship and a plane for a
long time. Since the gyroscope for military affairs or planes is
manufactured through a precision processing and an assembly process
of several thousands of the parts, a precise performance can be
obtained. However, since a manufacturing cost is high and the
structure of the gyroscope is bulky, it is not proper to apply the
gyroscope to home appliances for a general industry or public
needs. The gyroscope used for public needs can be applied to a
navigation device for detecting the acceleration and angular
velocity of a car or a device for detecting the wobbling of a hand
when using a high magnification camcorder to compensate for the
wobble of the operator's hand. Also, a sensor incorporating a
dual-axis vibratory structure is used in medical equipment or
measuring instruments for industry.
FIG. 1 shows the gyroscope using the dual-axis vibratory structure
schematically. The principle of the gyroscope is to detect a
rotation angular velocity by detecting a Coriolis force generated
in a third axis direction perpendicular to a first and a second
axis direction, when the inertial body oscillating or rotating
uniformly in the first axis direction receives the rotation angular
velocity in the second axis direction perpendicular to the first
axis direction.
A gyroscope 10 is comprised of a dual-axis vibratory structure 12
disposed on the upper portion of a silicon wafer substrate 11. Any
material having a conductivity can be used as the structure 12. The
structure 12 is supported on the silicon substrate 11 by a
supporting portion 13 formed slightly thicker than the other
portion, the other portion except the supporting portion 13 is
formed thinly to be in a state spaced in a Z axis direction from
the surface of the silicon substrate 11. Spring portions 14,15 and
16 and a mass portions 17 are provided in the structure 12. Driving
portion 21 for oscillating the structure 12 in a X direction are
disposed on both sides of the structure 12. The driving portions 21
are also formed of a conductive material. If a current is supplied
to the driving portions 21 being a type of an electrode, an
electrostatic force is generated in a finger 22 of driving porions
21 to thereby cause a vibrating movement from a finger 19 of the
structure 12. A surface sensor electrode (not shown) capable of
detecting the displacement of the Z direction of the structure 12
is disposed on the lower portion of the structure 12. The
displacement of the Z direction of the structure 12 can be measured
from the change of capacitance generated in the surface sensor
electrode.
The angular velocity of the rotating inertial body in Y axis
direction is obtained as follows. While the current is supplied to
the finger 22 to generate a vibration in the X direction of the
structure 12 with the electrostatic force, the frequency of the X
direction is measured from a center sensor electrode 23 located at
a central portion of the vibratory structure 12. Also, if the
structure 12 vibrates in the Z axis direction by the Coriolis
force, the frequency of the Z direction is measured from the
surface sensor electrode disposed on the lower portion of the
structure 12. The frequencies of the X axis direction and the Z
axis direction measured as above are data-processed and thus it is
possible to get the angular velocity of the rotating inertial
body.
As explained above, the gyroscope 10 includes the vibratory
structure provided with the silicon substrate 11 and the mass
portion 17 through the springs 14,15 and 16 to the supporting
portion 13 fixed thereon, and the mass portion 17 vibrates in the
X-axis and Z-axis directions. Accordingly, the gyroscope 10 has a
natural frequency on two axes. At this time, in order to guarantee
the performance of the gyroscope, the natural frequency on a
dual-axis vibration of the structure 12 should be within the range
of a preset error. However, if the structure 12 is manufactured by
using the conventional technology such as an etching or chemical
vapor deposition process, a processing error of usually
0.1.about.1.0 .mu.m appears in the manufacturing process. Due to
such an error of the manufacturing process, the spring constant of
the structure 12 and the mass of the mass portion 17 are
considerably deviated from a design value so that the natural
frequency of two axes direction differs from a desired value.
Accordingly, there is a problem in that the performance of the
gyroscope deteriorates. In order to solve the above problem, a
method of adjusting properly the spring constant of the springs
14,15 and 16 in the structure 12 is needed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel method
capable of adjusting the frequency of a dual-axis vibratory
structure.
It is another object of the present invention to provide a method
capable of adjusting the natural frequency of one axis of the
dual-axis vibratory structure while fixing the natural frequency of
the other axis.
It is still another object of the present invention to provide a
method capable of adjusting the natural frequency of the dual-axis
vibratory structure for use in a vibratory gyroscope.
To accomplish one aspect of the above object, there is provided a
method of adjusting the natural frequency of a dual-axis vibratory
structure having: a first spring member having a lengthwise
direction coinciding to a first axis direction receiving an
electrostatic force; a second spring member having a lengthwise
direction coinciding to a second direction perpendicular to the
first axis direction and having a width narrower than that of the
first spring member; and a mass portion, said method comprising the
steps of:
measuring the natural frequencies relative to the first axis
direction of the vibratory structure and a third axis direction
perpendicular to a plane formed by the first and second axes;
varying the thickness of the first spring member so as to adjust
the natural frequency of the third axis direction while fixing the
natural frequency of the first axis direction; and
repeating said measuring step and said thickness varying step until
the natural frequencies of the first and third axes directions are
within the scope of a permissible error.
According to another characteristic of the present invention, there
is provided a method of adjusting the natural frequency of a
dual-axis vibratory structure, wherein said thickness-varying step
includes the step of decreasing the thickness of the first spring
member, when the natural frequency of the third axis direction of
the structure is higher than that of the first axis direction.
According to another characteristic of the present invention, there
is provided a method of adjusting the natural frequency of a
dual-axis vibratory structure, wherein said thickness-varying step
includes the step of increasing the thickness of the first spring
member, when the natural frequency of the third axis direction of
the structure is lower than that of the first axis direction.
According to another characteristic of the present invention, there
is provided a method of adjusting the natural frequency of a
dual-axis vibratory structure, wherein the thickness-decreasing
step is executed by one of reactive ion etching, plasma etching and
sputtering.
According to another characteristic of the present invention, there
is provided a method of adjusting the natural frequency of a
dual-axis vibratory structure, wherein said thickness-increasing
step is executed by one of sputtering deposition, ion beam
sputtering deposition, electron-cyclotron-resonance sputtering
deposition, ion-plating, molecular beam epitaxy, chemical vapor
deposition, and metal organic chemical vapor deposition.
According to another characteristic of the present invention, there
is provided a method of adjusting the natural frequency of a
dual-axis vibratory structure, wherein said thickness-varying step
is executed by using a mask formed with an aperture corresponding
to a region for realizing a thickness variation in the first spring
member and by varying the thickness of the first spring member
under the aperture.
To accomplish another aspect of the present invention, there is
provided a method of adjusting the natural frequency of a dual-axis
vibratory structure, for use in a gyroscope, having: a first spring
member of a first axis direction coinciding with the direction
receiving an electrostatic force; a second spring member of a
second axis direction perpendicular to the first direction having a
width narrower than that of the first spring member; and a mass
portion, said method comprising the steps of:
measuring the-natural frequency relative to the first axis
direction and the third axis direction perpendicular to a plane
formed by the first and second axes of the vibratory structure;
varying the thickness of the first spring member of the first axis
direction so as to adjust the natural frequency of the third axis
direction, while fixing the natural frequency of the first axis
direction; and
repeating said measuring step and said thickness varying step until
the natural frequency of the first axis direction and the third
axis direction is within the scope of a predetermined error.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and advantages of the present invention will
become more apparent by describing in detail a preferred embodiment
thereof with reference to the attached drawings in which:
FIG. 1 is a perspective view of a dual-axis vibratory structure
installed in a gyroscope according to a conventional
technology;
FIG. 2 is a graph showing the natural frequency of an X axis and a
Y axis of the dual-axis vibratory structure in FIG. 1;
FIG. 3 is a perspective view for explaining a method of adjusting
the natural frequency of a dual-axis vibratory structure, according
to the present invention; and
FIGS. 4A and 4B are sectional views taken along the line A-A' of
FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
To assist understanding of the present invention, a frequency
response of the dual-axis vibratory structure 12 will be described
with reference to FIG. 1 and 2. In the graph of FIG. 2, there are
two response curves, namely, a frequency response curve 25 of the X
axis direction and a frequency response curve 26 of the Z axis
direction. The natural frequencies of the vibratory structure are
indicated as f.sub.x and f.sub.z relative to the X axis and the Z
axis, respectively. Here, the natural frequencies f.sub.x and
f.sub.z for either axis are functions of mass and the elastic
modulus of a spring (spring constant), thus: ##EQU1## where k.sub.x
and k.sub.z are equivalent spring constants (for one and the other
axis directions) of the spring portions 14,15 and 16, and m is the
mass of the mass portion 17. Here, though the true value of m would
be equal to the total mass of the mass portion 17 and the spring
portions 14, 15 and 16, mass m can be taken as the mass of the mass
portion 17 only, since the collective mass of the spring portions
is generally regarded as negligible in comparison with that of the
mass portion itself.
Generally the dual-axis vibratory structure includes a spring
portion 15 having a wide width in one direction where the
electrostatic force is applied by a driving electrode, while the
vibratory structure includes the spring portions 14 and 16 having
narrow widths in the other direction. If the thickness of the
spring portions 14, 15 and 16 varies, the spring constants relative
to the X axis and the Z axis also vary.
In order to secure the performance of the dual-axis vibratory
structure 12, an adjustment should be performed to vary the Z-axis
natural frequency f.sub.z while fixing the natural frequency
f.sub.x of the X direction. However, in consideration of the shape
of the structure 12 shown in FIG. 1, if the thickness of the
(narrow) spring portions 14 or 16 varies, there is a problem in
that the spring constants of both directions vary together. On the
other hand, if the thickness of the (wide) spring portion 15
varies, only the Z-axis spring constants can be varied, with nearly
no variation of that of the X axis direction. In the present
invention, on the basis of the above point, the thickness of a
spring portion 15 having a wide width varies so as to adjust the
Z-axis natural frequency f.sub.z, while fixing the natural
frequency f.sub.x of the X direction.
FIG. 3 is a diagram for explaining the method of adjusting the
natural frequency of a dual-axis vibratory structure 32 according
to the present invention. The vibratory structure 32 is provided
with a spring portion 36 having a wide width in the X direction,
springs 34 and 35 having narrow width in the Y direction, and a
mass portion 37. The variation of the thickness of the spring
portion 35 having the wide width is realized by depositing
different material on a predetermined region 39 or etching part of
the region 39, by using a mask 41. Widely used deposition methods
include sputtering deposition, ion beam deposition,
electron-cyclotron-resonance sputtering deposition, ion plating
deposition, atom beam epitaxy, chemical vapor deposition, and metal
organic chemical vapor deposition. The part of the spring portion
can be removed by reactive ion etching (widely used in
semiconductor processing). For example, with a pressure of about
0.01.about.0.10 Torr, if CF.sub.4 gas is used, the etching can be
realized at a speed of 0.05.about.1.00 .mu.m per minute. Besides
reactive ion etching, the thickness of the spring portion 35 can be
varied using plasma etching or sputtering etching. The mask 41 has
a plurality of apertures 42 formed to correspond to the region 39
needed to vary the thickness of the spring portion 35. FIGS. 4A and
4B show the cross-section taken along the line A-A' of FIG. 3. FIG.
4A shows a part 39A of the spring portion removed by etching, while
FIG. 4B shows a part 39B of the spring portion risen by
depositing
The adjustment of the natural frequency resulting from the
variation of the thickness of the spring portion 35 is carried out
with a trial and error method. After the structure 32 is
fabricated, the natural frequency relative to each axis direction
is measured. As stated above referring to FIG. 1, the measurement
of the natural frequency relative to the X axis direction is
carried out by using the center sensor electrode 23 located at the
central portion of the structure and the measurement of the natural
frequency relative to the Z axis direction can be carried out by
using a surface electrode (not shown) disposed on the substrate 11.
It is preferable that the natural frequencies of two axes coincide
with each other, but the natural frequencies may not coincide
within a predetermined scope in design. When the measured natural
frequencies are compared with each other resulting in that f.sub.z
is higher than f.sub.x, the etching operation is performed as shown
in FIG. 4A, to reduce the value of the Z-axis spring constant so
that f.sub.z can be reduced. On the contrary, the deposition
operation is performed as shown in FIG. 4B to increase f.sub.z. If
the etching or deposition operation is terminated, it is measured
whether or not the natural frequency relative to each axis
direction is within the scope of a predetermined error, otherwise
the operation as above is repeatedly performed.
The method of adjusting the natural frequency of a dual-axes
vibratory structure according to the present invention can adjust
the natural frequency of the vibratory structure to coincide with a
design value so that linearity and the sensitivity of a sensor are
improved and operation bandwidth increases. Also, the frequency
error of the vibratory structure can be adjusted to improve
performances of a gyroscope, an angular velocity sensor and an
acceleration sensor using the vibratory structure.
While the present invention is explained with reference to one
embodiment shown in drawings, it is understood that a number of
alterations can be made by those of ordinary skill in the art.
Accordingly, the true scope of protection of the present invention
is determined by the scope of the attached claims.
* * * * *